Treatment of waste liquors



Patented Dec. 1, 1931 UNITED STATES PATENT OFFICE RUPERT SYDNEY JONES,OI FLINT, AND STANLEY PEARSON, 0F COV ENTRY, ENGLAND, ASSIGNOBS TOCOUB'IAULDS LIKITED, OI IDNDON, ENGLAND, ABRITISH COMPANY TBEATIEN'I OIWASTE LIQUORS i No Drawing. Application fled July 15, 1830, Serial No.488,199, and in Great Britain September 23, 1929.

This invention relates to the treatment of waste liquors and inparticular to waste liquors containing alkahne sulphide, including inthis term both monoand oly-sulphide. Such waste liquors cannot be'scharged directly into streams or small rivers on account of the toxicaction of the alkaline sulphides, and therefore it becomes necessaryfirst to remove such alkaline sulphides. A method hitherto employed forthis purpose has con sisted in treating the efiiuent liquors withferrous sulphate and milk of lime in order to precipitate the sulphidesin the form of fer- .rous. sulphide, and then to allow'the ferroussulphide so obtained to settle to ther with the lime, whereupon theclear uid, fre'e from the dissolved sulphide can, wit or without anysuch further treatment as may be considered desirable, be passed intothe stream or river.

We have now found that waste liquors containing alkaline sulphide asaforesaid, can be treated otherwise than hereinbefore described, wherebcertain advantages are obtained. Accor ing to this invention, the wasteliquors containin alkaline sulphide are treated with acid unti they areneutral or very slightly acid in the presence of a bodycontaining thesulphur dioxide radical.

They are then thoroughly mixed and then treated, in the presence of azinc or magnesi um compound, with caustic'alkali unt1l the whole liquoris alkaline, and preferably alkaline to phenol phthalein.

If the waste liquors already contain a boudfy containing the sulphurdioxide radical in s ficient quantity, it will be unnecessary to add afurther quantity of such body. In case however, there is an insufiicientamount of 0 such body present, so that after addin the acid there is notenough sul liur dioxi e to combine with the whole of t e sulphurettedhydrogen liberated, it will be necessary to add a bod containing thesulphur dioxide radicaL, is examples of bodies containing the sulphurdioxide radical we may mention a sulphite, such as sodium sulphite andsodiumvbisulphite, or sulphur dioxide itself can be emplo ed. Thesulphur dioxide may for example blown into the liquor in the form ofgas, or the sulphur dioxide can be. made to react with the li nor in atower. It is pre ferred that the b0 y containing the sulphur dioxideradical be present in the waste liquors before the acid he added or thatit be added simultaneously with the acid. In some cases however, thebenefits of this invention can be obtained by adding the body containingthe sulphur dioxide radical soon after the addition of the acid to thewaste liquors.

As examples of zinc or magnesium comounds which can be used according tothis invention, we may mention salts such as zinc sulphate but othercompounds such as magneslum oxide and magnesium hydroxide can also beemployed. The zinc or magnesium compound and the caustic alkali can beadded tothe waste li uor simultaneously, or they may even be a dedtogether in the form of I sodium zincate; it is generally preferredhowever, to add the zinc or magnesium compound earlier in the process,for example simultaneously with the'body containing the sulphur dioxideradical since an eflicient mixing is acid. The liquors are then passedthrough a tank whereby they become thoroughly mixed,

I whereupon a portion of the precipitated sulphur W111 settle out;caustic alkali is then added until the whole liquor is alkaline, andpreferably alkaline to phenol phthalein. The alkaline liquor isthen'passed through prec'ipitating tanks, whereupon the prom ltated zinchydrate and the remainder of t e sul- 2 a -v ..1,es4,e45

phur settle out very effectively, leaving. a '1 clear efiluent liquorfree from the dissolved sulphide. e. The sulphur which settles from theliquor 5 during th1s process can advantageously be used as a source ofthe sulphur dioxide'radical which is used in treating further wasteliquors. The zinc or magnesium compound used may bedefined as a compoundof a metal of the magnesium group with an atomic wei ht between 20 and70.

hat we claim is 1-. The treatment of waste liquors containing: alkalinesulphide which consists in first treatin the said liquors with acidinthe presence o a body containingthe sulphur dioxide radical, and thenwith caustic alkali, in i c the presence of a compound of the magnesiumgroup with anatomic weight between 20 and 70 until the whole liquor isalkaline,

substantially as described.

l 2. The treatment of waste liquors contain.-

- ing alkaline sulphide which consists in treating the said liquors withacid until they are 5 neutral or very slightly acid, and adding acompound of the magnesium, group with an atomic weight between 20 and'70 and a body containing the sulphur'dioxide radical, then passing theliquors through a tank and allowing a part of the sulphur to settle out,then adding caustic alkali until the wholeli uor is'alkaline and thenpassing the alkaline quors through further precipitating tanks.

In testimony whereof we have signed our names to this specification.

RUPERT SYDNEY LI' NES. STANLEY PEARSON.

